Turnover is a major concern for organizations due to the high financial costs associated with recruiting and training replacement staff. In the substance use disorder (SUD) treatment field, turnover also is a concern due to higher than average rates of turnover and the belief that turnover negatively impacts quality of care and treatment outcomes for treatment patients. However, due in part to the difficulty of collecting treatment outcome data linked to therapist data, no research to date has explicitly examined the relationship between therapist turnover and patient treatment outcomes. Using existing data collected within the context of a large health services demonstration project, which includes data from 3,021 adolescent patients, 208 therapists, and 34 organizations, the proposed study would be one of the first known studies to quantify the direct and indirect impact of therapist turnover on quality of care and treatment outcomes of patients. Regardless of whether or not therapist turnover negatively impacts treatment quality and outcomes for patients, the financial costs of turnover alone suggest the need to improve our knowledge regarding factors that lead to turnover. Although hundreds of turnover-related studies have been conducted, a major limitation of most of the existing literature is that it has relied primarily on cross-sectional methods of investigation. Thus, in order to better understand the process of staff turnover more fully, the proposed study will use existing repeated measures therapist data to examine longitudinal predictors and mediators of turnover. Identification of factors that lead to turnover may be invaluable in developing testable strategies for reducing turnover and subsequent financial costs. PUBLIC HEALTH RELEVANCE: Within human service organizations, staff turnover is thought to not only have significant financial costs, but have a significant adverse impact on the quality of care and treatment outcomes for patients. The proposed study is highly relevant, as it would be the first known study with the substance use disorder field to (a) quantify the direct and indirect impact of therapist turnover on treatment quality and outcomes and (b) use longitudinal data collection methods and analyses to identify factors that lead to therapist turnover.